DESCKIPTION OF A NEW SPECIES OF COTTON RAT (SIGMODON MINIMA) FROM NEW MEXICO.
By Edgak a. Mearns, M. D.,Surgeon, United States Army.
Among the .small uiaminaLs collected by Mr. F, X. Holzner and myselfon the Mexican border, in coimection with the operations of the Inter-national Boundary Commission, are two specimens of a species of cot-ton rat, which, in my opinion, is distinct from any heretofore described.In the grassy hollows and fiats between the most southern spurs ofthe Apache Mountains, in an arid, treeless region, having an altitudeof 1,500 metres (exactly l,49(j at the monument), it was a surprise tofind any species of SU/niodoH. Many of their old runways were seen,however, in the dry and dusty grass; but nearly all of the holes wereabandoned. Industrious trai)piug, persisted in for several weeks,resulted in the capture of but two adult male specimens. Mexicanminers in the vicinity told us that only a few months before the specieshad been abundant, but seemed to have died off; indeed, we frequentlysaw their remains in tbe grass and i)icked up parts of skeletons andone or two additional skulls.This new species has many points in common with Sigmodon fal-viventer, recently described by Dr. J. A. Allen, from Zacatecas, Mex-ico.* It is still smaller than that species, being about the size of DeSaussure's ^^ Hesperomys toltecus^^ {= Sigmodon hispidus toliecvs).\ Oncapturing these specimens I was at once struck by their resemblance toS. fulviventer, the type of which I had closely examined in the AmericanMuseum of Natural History in New York, the lesemblance consistingnot only in the fulvous tone of coloring, especially of the under parts,but in the distinctly bristly character of the hairy coat and the densehairiness of the ears and tail, in all of which particulars it differs
* Bull. Amer. Mus. Nat. Hist., ii. No. 3, p. 180, October 21, 1889.t Alleu. /.. c, III, 1891, p. 207.
* Proceedings National Museum, Vol. XVII?No. 994. 129Proc. N. M. 04 9
130 A NEW SPECIES OF COTTON BAT?MESENS. vol.xvii.
radically from its geographically nearest neighbors
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Sigmodon hispidustexianus, (And. and Bach.) and ;S'. hispidus arizonw, (Mearns).SIGMODON MINIMA, iimw species.Type.?^o. 2L1S7, U. S. N. M. (Coll. International Boundary Commis-sion). Adult male, from Upper Corner Monument, New Mexico, on theMexican boundary line, 100 miles west of the initial monument on thewest bank of the Rio Grande. Collected by Edgar A. Mearns andFrank X. Holzner, April 26, 1892.Description of type.?Coat bushy and hispid; under-fur darker plum-beous than in S. hispidus texianus or 8. liispidus arizonce; coarse outercoat more bristly, especially on sides of head and neck; ears, feet, andtail densely hairy; tail not distinctly bicolor. Color above grayish, theindividual hairs being ringed with gray and brown, the brown annulibeing blackish in their middle portion, fading to light-yellowish brown ontheir edges ; under surface of body clayey buff; feet yellowish gray
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ears densely clothed with grayish hairs on inner surface, with theirconvex surface black anteriorly and buff posteriorly; tail brownishblack, somewhat lighter below, the hairs almost concealing the annuli.Another specimen (No. 1760, male adult, from the same locality, col-lected by Mearns and Holzner, May 13, 1892) differs only in beingochraceous buff below, with a little more of the fulvous tinge on rumpand flanks, thus approaching more closely to the coloration of Sigmodonfulviventer.Dimensions.?Measurements (in millimeters) of No. 21187, adult male:Length, measured from nose to end ofvertebrte of tail, 223; tail, measuredfrom root to end of vertebric, 94; to end of hairs, 104; height of ear abovecrown, 14; distance between eyes, 12; diameter of eye, 5; length oflongest whisker, 30; from tip of nose to eye, 16; to center of pupil, 18.5;to ear, 30; to tip of ear, 46; to occiput, 37; to end of outstretched hindlimb, 183; fore limb, measured from olecranon to end of longest claw, 33;length of fore-foot, 15; longest claw of fore-foot (chord), 3.9; hind limb,measured from knee-joint to end of longest claw, 53; length of hind-foot,28; longest claw of hind-foot, 3 mm. Measurements of No. 1700, adultmale : Length, 223 ; tail to end of vetebra;, 91 ; to end of hairs, 97 ; heightof ear above crown, 12; above notch, 16; distance between eyes, 12;diameter of eye, 5; longest whisker, 26; from top of nose to eye, 16; tocenter of pupil, 19; to ear, 30; to tip of ear, 46; to occiput, 34; to end ofhinder extremity, 180; fore limb from olecranon, 33; length of fore-foot,14; longest claw of fore-foot, 3 ; hind limb from knee-joint, 53; length ofhind-foot, 27; longest claw of hind-foot, 4.2 mm.Cranial and dental characters.?As comi)ared with S. hispidus texianus,the only species before me for comparison, the brain-case is higher andnarrower, the skull more constricted between the orbits, with shorternasals, their bases being nearly even with the posterior border of theincisive foramen instead of well behind it. The dentition is very muchheavier.